In centrifugal rotary machines such as centrifugal compressors, there has been market demand for an increase in performance through improvement of a head, expansion of an operating range, or the like, and thus various measures have been taken, for the demand.
Here, in a flow path of an impeller used for the centrifugal rotary machine, a flow flowing in a direction different from a main stream, i.e., a secondary flow, may occur in some cases. Due to the secondary flow, a low energy fluid is accumulated in the flow path of the impeller and speed and energy of the fluid of the accumulated portion become considerably deficient. For this reason, such a secondary flow is one factor that degrades performance of the centrifugal rotary machine.
Patent Literature 1 discloses an impeller for a centrifugal compressor in which performance is improved by suppressing a secondary flow flowing from a pressure side toward a suction side of a blade in an impeller. Specifically, in the impeller, a boundary layer flow in a side wall surface of a flow path prevents the secondary flow from flowing to transect the flow path from the pressure side to the suction side of the blade with a riblet installed along a flow of a main stream from the side wall surface.